Method of depositing metallic copper



March 28, 1961 s. E. KAY ET AL METHOD OF DEPOSITING METALLIC COPPER Filed Jan. 50, 1959 by spraying, brushing or other methods.

METHOD OF DEPOSITING METALLIC COPPER Solomon Elijah Kay and Robert John Ball, St. Helens,

England, assignors to Pilkington Brothers Limited, Liverpool, England Filed Jan. 30, 1959, Ser. No. 790,119 a 7 Claims priority, application Great Britain Feb. 1, 1958 17 Claims. (Cl. 117-71) The present invention is concerned with an improved method of depositing a layer of metallic copper on a surface, and is especially concerned with an improved method of applying a protective copper coating to the silvered surface of a mirror.

In the production of silvered mirrors it is the usual practice to apply a silvered surface to one side of a sheet of plate glass, to wash the silver layer and then to transfer the mirror to a copper electro-plating bath where the silver coating is made an electrode and has deposited thereon a protective layer of copper. The copper layer is then itself protected by applying thereto a suitable paint The handling of the freshly silvered mirror without damaging the thin reflective surface is a serious practical problem. The silver layer is easily scratched or rubbed off and this is particularly likely to occur when electrical connection is made to the silver surface in the copper-plating bath. In addition if the copper-plating electrolyte is not thoroughly removed from the plated surface after plating, it may give rise to deterioration of the mirror.

In order to avoid the disadvantages inherent in the application of the protective copper coating by electroplating, it has been proposed that this coating should be formed by spraying an aqueous acidic solution of a copper salt, such as copper sulphate, and an aqueous dispersion of a finely divided metal higher than copper in the electro-negative series, such as zinc or iron, onto the silvered surface. The copper salt solution and the metal react on the surface with displacement of metallic copper from the copper salt by the more electro-negative metal and consequent formation of a layer of metallic copper.

It is a'main object of the present invention to provide an improved method of depositing a protective layer of metallic copper onto a silvered surface which avoids the maintenance of a uniform aqueous dispersion of the more electro-negative metal.

The present invention is based on the observation that aqueous solutions of cuprous salts are only stable when such salts are in complex form and that if a solution of a complex cuprous salt is rendered acidic, metallic copper is deposited and a soluble cupric salt is formed.

A method of depositing a layer of metallic copper on a surface accordingto the invention comprises .separately spraying an aqueous solution of a complex cuprous salt and an aqueous acid solution simultaneously towards the surface so as to mix-the two-solutions and thereby deposit a layer of metallic copper thereon. 7

The invention also comprises a method of 'tiepositing a protective layer of met-allic-copperon a silveredrrriirror,

which comprises separately spraying an aqueous solution of a complex cuprous salt and an aqueous acid solution simultaneously towards the silvered surface so as to mix the two sprayed solutions and thereby deposit a layer of metallic copper on the surface.

In applying a protective layer of metallic copper to a silvered surface the said solutions are preferably sprayed States Patent G ice towards the silvered surface immediately after "the latter has been deposited and while it is still wet.

The solutions may be sprayed onto the surface in such a way that mixing of the solutions takes place at the surface, but it is generally preferred that the two spray streams should be so directed that they coincide in front of the surface and the mixed stream thus formed is directed onto the surface. In either case the method according to the invention'is' advantageously effected by projecting individual jets of the aqueous solution of the complex cuprous salt and the aqueous acid solution in the form of droplets from opposite sides of a continuous jet of air under pressure directed substantially perpendicularly towards the surface so as to coincide with the jet of air under pressure at, or in front of, the surface.

The aqueous acid solution may he a solution of any suitablecrganic or inorganic acid and .is preferably a dilute solution of a .mineral'iacid. The solution of the complex cuprous salt .may beprepared, for example, by adding metallic copper powder to anammoniacal copper sulphate solution. Alternatively it maybe an ammoniacal solution of cuprous oxide in aqueous ammonium sulphate.

In order that the invention may be clearly understood an embodiment of apparatus for carrying it into effect will now be described by way'of example with reference to the accompanying diagrammatic drawing which illustrates apparatus for depositing a layer of metallictcopper on a silvered mirror.

By way of example, the composition of typical working solutions for use 'in the method according to themvention, is as follows:

(a) Solution of complexcuprous salt Cuprous'oxide gms '10 Ammonium sulphate gms-.. '30 Ammonia (0.880) ccs '25 Water to 1 litre.

'cu 0+2NH ++2NH,- 2rcu Y(NH3)2] +11 0 (b) Acid solution -5 gm. concentrated sulphuric acid were-made up 1 litre with water.

In operation, the solution of the complex-cuprous salt (a) was used at the rate of ccs./min./sq. :foot to be processed :and :the acid solution ccs./min./sq. foot to be processed.

Since inpractice the'area covered by the spray which is directed onto the surface may be considerably smaller than the area to be coated with metalliccopper, it vmay be necessary that the zone containing the mixed solutions be caused to travel successively overt-he whole of the surface to be coated.

In one method of effecting this as illustrated .in #the accompanying diagrammatic drawing, anarticle '1 whose surface is to be coated, for example asilvered mirror surface, is carried on a conveyor belt 2. Spray heads 3 and 4 adapted to deliver the separatespray streams idepend from acarriage 5, which is formed asitwoseparate chambered and .7. I The spray heads 3 ends! arespectively (b) :at' *the rate "of 200 along the rails 10 by a cam mechanism which includes a rod 11 supported in a collar 12, one end of the rod 11 being fixed to the carriage and the other carrying a cam follower 13 which engages the surface of a cam 14. A spring 15 extends between the collar 12 and a flange 16 on the rod 11 to maintain the cam follower 13 in contact with the cam surface.

As the cam 14 rotates the spray heads 3 and 4 are reciprocated at right angles to the direction of movement of the Conveyor belt 2, so that successive transverse bands 11 of the surface are coated with metallic copper by reaction between the two solutions:

In this method of operation, the amount of copper deposited on the surface depends on the relative rates of travel of the conveyor belt and the carriage, and also on the rates of flow of the two solutions. v

Alternatively, the carriage 5 may be extended at right angles to the conveyor belt 2 and a number of spray heads provided communicating with each of the chambers 6 and 7 and arranged across the conveyor belt 2 so that reciprocation can be dispensed with. Suitable adjustment of the conveyor belt speed would be necessary.

It will be appreciated from the foregoing description .that in the method according to the invention, the mechanical problems involved in delivering a uniform aqueous metallic dispersion, as required by the heretofore proposed spray coppering method referred to above, do not arise as solutions only are employed. Furthermore the only insoluble material produced is the desired metallic copper and there is no possibility of copper alloy formaaqueous solution of a complex cuprous salt and an aqueous acid solution simultaneously towards the surface so as to mix the two solutions and thereby deposit a layer of metallic copper on the surface.

2. A method according to claim 1, in which the solution of a complex cuprous salt is prepared by adding metallic copper powder to an ammoniacal copper sulphate solution.

' 3. A method according to claim 1, in which the solution of a complex cuprous salt is an ammoniacal solution of cuprous oxide in aqueous ammonium sulphate.

4. A method according to claim 1, in which the aqueous acid solution is a dilute solution of a mineral acid.

5. A method of depositing a protective layer of metallic copper on a silvered mirror, which comprises separately spraying an aqueous solution of a complex cuprous salt and an aqueous acid solution simultaneously towards the silvered surface so as to mix the two sprayed solutions and thereby deposit a layer of metallic copper thereon.

6. A method according to claim 5, in which said solutions are sprayed towards the silvered surface immediately after the latter has been deposited and while it is still wet.

7. A method according to claim 6, in which the solution of a complex cuprous salt is prepared by adding metallic copper powder to an ammoniacal copper sulphate solution, and the aqueous acid solution is a dilute solution of a mineral acid.

8. A method according to claim 6, in which the solution of a complex cuprous salt is an ammoniacal solu tion of cuprous oxide in aqueous ammonium sulphate, and the aqueous acid solution is a dilute solution of a mineral acid.

9. A method of depositing a layer of metallic copper on a surface which comprises separately spraying an aqueous solution of a complex cuprous salt and an aqueous acid solution simultaneously towards the surface in such a, manner that the two spray streams are mixed in front of the surface and the mixed stream is directed onto the surface to deposit a layer of metallic copper thereon.

10. A method of depositing a protective layer of metallic copper on a silvered mirror which comprises separately spraying an aqueous solution of a complex cuprous salt and a dilute solution of a mineral acid simultaneously towards the silvered surface in such a manner that the two spray streams are mixed in front of the surface and the mixed stream is directed on to the surface to deposit a protective layer of metallic copper thereon.

11. A method according to claim 10, in which the solutions are sprayed towards the silvered surface immediately after the latter has been deposited and while it is still wet.

12. A method of depositing a layer of metallic copper on a surface, in which separate jets of an aqueous alkaline solution of a cuprous compound and a dilute solution of a mineral acid are projected in the form of droplets from opposite sides of a continuous jet of air under pressure directed substantially perpendicularly towards the surface so as to coincide with the jet of air under pressure at the surface;

13. A method according to claim 12, in which the cuprous complex solution is prepared by adding metallic copper powder to an ammoniacal copper sulphate solution.

14. A method according to claim 12, in which the cuprous complex solution is an ammoniacal solution of cuprous oxide in aqueous ammonium sulphate.

15. A method of depositing a protective layer of metallic copper on a silvered mirror, in which separate jets of an aqueous alkaline solution of a cuprous compound and a dilute solution of a mineral acid are projected in the form of droplets from opposite sides of a continuous jet of air under pressure directed substantially perpendicularly towards the surface so as to coincide with the jet of air under pressure in front of the surface.

16. A method according to claim 15, in which the cuprous complex solution is prepared by adding metallic copper powder to an ammoniacal copper sulphate solution.

17. A method according to claim 15, in which the cuprous complex solution is an ammoniacal solution of cuprous oxide in aqueous ammonium sulphate.

References Cited in the file of this patent UNITED STATES PATENTS 2,664,363 Meth Dec. 29, 1953 2,748,023 Meth May 29, 1956 2,768,944 Meth Oct. 30, 1956 2,815,298 Heflley Dec; 3, 1957 

5. A METHOD OF DEPOSITING A PROTECTIVE LAYER OF METALLIC COPPER ON A SILVERED MIRROR, WHICH COMPRISES SEPARATELY SPRAYING AN AQUEOUS SOLUTION OF A COMPLEX CUPROUS SALT AND AN AQUEOUS ACID SOLUTION SIMULTANEOUSLY TOWARDS SILVERED SURFACE SO AS TO MIX THE TWO SPRAYED SOLUTIONS AND THEREBY DEPOSIT A LAYER OF METALLIC COPPER THEREON. 